1. Field of the Invention
The present invention relates to a focus detecting device and a method for positioning and fixing an optical member and a holding member holding the optical member.
2. Description of Related Art
The conventional arrangement of a focus detecting device necessitates a focus detecting sensor thereof to be swingable with respect to a reimaging lens secured to the body block of the focus detecting device for the purpose of performing positional adjustment such as adjustment of the optical axis and inclination of the focus detecting sensor.
To meet this requirement, a conventional focus detecting sensor of the type using a clear mold is, for example, arranged as described below. The clear mold used for the focus detecting sensor is first explained with reference to FIGS. 7(a) and 7(b).
FIG. 7(a) shows the clear mold in a plan view. FIG. 7(b) shows the clear mold in a sectional view taken on a line A-Axe2x80x2 of FIG. 7(a).
Referring to FIGS. 7(a) and 7(b), a focus detecting sensor 301 is positioned at a lead frame 302 and connected to the lead frame 302 by wire bonding in a known manner. A clear mold 300 is formed by molding a transparent resin with the focus detecting sensor 301 and the lead frame 302 inserted therein to be packaged together.
The clear mold 300 has a transparent resin part 304. Lead parts 303 are formed integrally with the lead frame 302. The lead parts 303 are connected to a mounting member 305 by soldering or the like.
A glass plate 306 is applied to the clear mold 300 on the sensor side thereof so as to protect the optical path of the focus detecting sensor 301 from being damaged, because the optical path tends to be damaged if the transparent resin part 304 on this side of the clear mold 300 is left uncovered.
The clear mold 300 which is arranged in this manner is held in a position-adjustable state by a sensor holder which is adjustably aslant with respect to the reimaging lens. Therefore, the position of the clear mold 300 relative to the reimaging lens can be adjusted as desired. Further, the sensor holder is held by a body block of the focus detecting device in such a way as to permit adjustment of its position. The position of the focus detecting sensor is thus arranged to be adjustable with respect to the reimaging lens.
The arrangement described above thus permits adjustment of the focus detecting sensor to an optimum position relative to the reimaging lens by adjusting the relative positions of the focus detecting sensor and the sensor holder and those of the sensor holder and the body block of the focus detecting device. After the position of the focus detecting sensor is adjusted, the focus detecting sensor and the sensor holder are fixedly joined together by an adhesive while the body block of the focus detecting device and the sensor holder are fixedly joined together by bonding also with an adhesive.
It is a feature of the above-stated conventional arrangement that the bonding work on all these parts is performed after completion of position adjustment of the focus detecting sensor. Further, the conventional focus detecting sensor of the above-stated kind is arranged to use the clear mold 300. The clear mold 300 is mounted on the body bock of the focus detecting device in a state of being set on the sensor holder which is provided for holding the focus detecting sensor before the position adjusting work is performed. These parts are fixed by an instantaneous adhesive after the position adjustment. The clear mold package which serves as an outer packaging for the focus detecting sensor, the sensor holder which is arranged to fix the clear mold package and the body block of the focus detecting device which is arranged to fix the sensor holder are molded with plastic materials of the same kind. Therefore, they can be readily joined together with the instantaneous adhesive and yet to have a sufficient adhesive, or bonding, strength. The accuracy of automatic focusing, therefore, has been little affected by the adhesive strength. However, the use of the clear mold has presented some problems.
While the conventional focus detecting device thus excels in adhesive strength and accuracy of focus detection on one hand, it is extremely difficult to accurately position the focus detecting sensor 301 and the lead frame 302 in manufacturing the focus detecting device. Further, in molding the transparent resin part 304, dust and air foams tend to mix in the resin to greatly lower the yield of production. The poor yield causes an increase in cost. Further, the glass plate 306 must be used for protecting the lead part 303 and the side face of the sensor. The use of the glass plate 306 causes an increase in outside dimensions.
These problems may be solved by forming the focus detecting sensor in a chip-on-board package (hereinafter referred to as a COB package). The COB package has an advantages over the clear mold package in the following points.
The COB package is formed by sandwiching a focus detecting sensor chip mounted on a substrate (base board) between a glass plate and the substrate, and filling a space between the substrate and the glass plate with a resin material. Compared with the clear mold package, the COB package can be manufactured with a less degree of possibility of having dust and air foams mixed therein. Therefore, the COB package can be manufactured with better yield and at lower cost. Besides, a through-hole part which is used in the manufacture of the COB package can be used also as the lead part which is used for the clear mold. The COB package thus dispenses with the lead part. The use of the glass plate on the side surface of the sensor also causes the COB package to dispense with any protection glass plate, thereby making the outside dimension of the COM package smaller.
However, if the COB package is arranged to have exactly the same structural arrangement as the clear mold package, there arises the following problem.
Since the COB package is arranged in the same manner as the clear mold package to receive the sensor on the glass surface of the COB package and the receiving surface of the sensor holder which are approximately flat, position adjustment is possible. However, after position adjustment, fixing by bonding encounters a problem.
In the case of the clear mold package, the clear mold package and the sensor holder can be easily bonded and joined together with an instantaneous adhesive to have a sufficient adhesive, or bonding, strength because they are formed by molding with similar plastic materials. With a focus detecting device arranged to use the COB package, however, the glass surface and the plastic material have poor adhesive properties for each other and are not easily bondable. Besides, since it is necessary to cause an instantaneous adhesive to instantly flow to the sensor holder in the shape of a focus detecting unit, it has been impossible to confirm that the adhesive has flown to the whole sensor holder. Therefore, it has been impossible to ensure a sufficient flow of the adhesive to cover the whole sensor holder to give a sufficient bonding strength.
Further, it is conceivable to attain a sufficient bonding strength by using an ultraviolet curable resin material for the adhesive. However, the ultraviolet curable resin excessively contracts and shrinks when it dries to harden. Therefore, if the ultraviolet curable resin is. used for bonding a focus detecting sensor after position adjustment, the position of the focus detecting sensor would be caused to deviate from the adjusted position by the contraction of the resin adhesive taking place when the resin dries and hardens.
Besides, the ultraviolet curable resin has a relatively large expansion coefficient after it dries and hardens. The ultraviolet curable resin would greatly expand and shrink according to changes in ambient temperature. Therefore, the use of the ultraviolet curable resin for bonding the focus detecting sensor is not desirable.
The invention is directed to the solution of the problems of the prior art. It is, therefore, an object of the invention to provide a focus detecting device in which a focus detecting sensor is arranged in a COB package to permit reduction in cost and size and yet to have sufficient bonding strength and focus detecting accuracy.
To attain the above object, in accordance with an aspect of the invention, there is provided a focus detecting device which comprises a focus detecting sensor having a glass plate affixed to a surface thereof, and a holding member which holds the focus detecting sensor, wherein the holding member is provided with a first abutting surface on which the glass plate of the focus detecting sensor abuts, a second abutting surface on which a side surface of the focus detecting sensor abuts, and a groove, disposed between the first and second abutting surfaces, in which an adhesive for fixing the focus detecting sensor flows, so that the focus detecting sensor and the holding member can be reliably joined together.
The above and other objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in connection with the accompanying drawings.